ACPAtmospheric Chemistry and PhysicsACPAtmos. Chem. Phys.1680-7324Copernicus PublicationsGöttingen, Germany10.5194/acp-7-2585-2007The direct effect of aerosols on solar radiation based on satellite observations, reanalysis datasets, and spectral aerosol optical properties from Global Aerosol Data Set (GADS)HatzianastassiouN.12MatsoukasC.23DrakakisE.25Stackhouse Jr.P. W.6KoepkeP.7FotiadiA.24PavlakisK. G.28VardavasI.241Laboratory of Meteorology, Department of Physics, University of Ioannina, 45110 Ioannina, Greece2Foundation for Research and Technology-Hellas, Heraklion, Crete, Greece3Department of Environment, University of the Aegean, Mytilene, Greece4Department of Physics, University of Crete, Crete, Greece5Department of Electrical Engineering, Technological Educational Institute of Crete, Heraklion, Greece6Atmospheric Sciences, NASA Langley Research Center, Hampton, Virginia, USA7Meteorological Institute, University of Munich, Munich, Germany8Department of General Applied Science, Technological Educational Institute of Crete, Heraklion, Greece1605200771025852599This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.This article is available from http://www.atmos-chem-phys.net/7/2585/2007/acp-7-2585-2007.htmlThe full text article is available as a PDF file from http://www.atmos-chem-phys.net/7/2585/2007/acp-7-2585-2007.pdf

A global estimate of the seasonal direct radiative effect (DRE) of natural
plus anthropogenic aerosols on solar radiation under all-sky conditions is
obtained by combining satellite measurements and reanalysis data with a
spectral radiative transfer model and spectral aerosol optical properties
taken from the Global Aerosol Data Set (GADS). The estimates are obtained
with detailed spectral model computations separating the ultraviolet (UV),
visible and near-infrared wavelengths. The global distribution of spectral
aerosol optical properties was taken from GADS whereas data for clouds,
water vapour, ozone, carbon dioxide, methane and surface albedo were taken
from various satellite and reanalysis datasets. Using these aerosol
properties and other related variables, we generate climatological (for the
12-year period 1984&ndash;1995) monthly mean aerosol DREs. The global annual mean
DRE on the outgoing SW radiation at the top of atmosphere (TOA, &Delta;<i>F</i><sub>TOA</sub>)
is &minus;1.62 W m<sup>&minus;2</sup> (with a range of &minus;15 to 10 W m<sup>&minus;2</sup>,
negative values corresponding to planetary cooling), the effect on the
atmospheric absorption of SW radiation (&Delta;<i>F</i><sub>atmab</sub>) is 1.6 W m<sup>&minus;2</sup>
(values up to 35 W m<sup>&minus;2</sup>, corresponding to atmospheric warming),
and the effect on the surface downward and absorbed SW radiation (&Delta;<i>F</i><sub>surf</sub>,
and &Delta;<i>F</i><sub>surfnet</sub>, respectively) is &minus;3.93 and &minus;3.22 W m<sup>&minus;2</sup>
(values up to &minus;45 and &minus;35 W m<sup>&minus;2</sup>, respectively, corresponding
to surface cooling). According to our results, aerosols decrease/increase
the planetary albedo by &minus;3 to 13% at the local scale, whereas on
planetary scale the result is an increase of 1.5%. Aerosols can warm
locally the atmosphere by up to 0.98 K day<sup>&minus;1</sup>, whereas they can cool the
Earth's surface by up to &minus;2.9 K day<sup>&minus;1</sup>. Both these effects, which can
significantly modify atmospheric dynamics and the hydrological cycle, can
produce significant planetary cooling on a regional scale, although
planetary warming can arise over highly reflecting surfaces. The aerosol DRE
at the Earth's surface compared to TOA can be up to 15 times larger at the
local scale. The largest aerosol DRE takes place in the northern hemisphere
both at the surface and the atmosphere, arising mainly at ultraviolet and
visible wavelengths.